1. Field of the Invention
This invention relates to an electromagnetic wave detector for detecting electromagnetic waves or high energy radiations such as ultraviolet rays, infrared rays, rays of visible light, X rays, α rays or γ rays.
2. Related Background Art
Electromagnetic wave detectors adapted to directly or indirectly convert electromagnetic waves or high energy radiations such as ultraviolet rays, infrared rays, rays of visible light, X rays, α rays or γ rays into an electric charge by means of a semiconductor article and read the stored electric charge find applications particularly in the field of imaging apparatus.
U.S. Pat. No. 5,811,790, Japanese Patent Application Laid-Open No. 09-288184, U.S. Pat. No. 5,856,699, Japanese Patent Application Laid-Open No. 09-260626 and other patent documents describe an electromagnetic wave detector adapted to convert visible light obtained by transforming X rays or some other high energy radiations into an electric charge and read the stored electric charge.
U.S. Pat. No. 5,391,881 describes an electromagnetic wave detector adapted to directly convert electromagnetic waves or high energy radiations such as ultraviolet rays, infrared rays, rays of visible light, X rays, α rays or γ rays into an electric charge.
FIGS. 14A and 14B of the accompanying drawings show a schematic cross sectional view and a schematic plan view of a known detector having a layered structure of monocrystalline bulk X ray detecting sections and monocrystalline readout ICs.
Referring to FIGS. 14A and 14B, as high energy electromagnetic waves 108 such as X rays enter the detector, an electric charge is generated in semiconductor substrates 106 typically made of Si, GaAs, CdTe or HgI2 and transferred to readout circuits 116 of integrated circuit chips 110a and 110b by way of electrodes 114, bumps 120 and electrodes 119. Electrodes 134a through 134e and electrodes 130a through 130d as well as bumps 136 are provided to connect the semiconductor substrates 106 and the integrated circuit chips 110a and 110b. 
U.S. Pat. No. 5,198,673 describes a direct type sensor equipped with protection diodes. FIG. 15 of the accompanying drawings is a schematic block diagram of the read/reset circuit of a direct type sensor 160 having protection diodes as disclosed in the above patent document. Referring to FIG. 15, there are shown scan switches 222a and 222b connected to scan wires 220a and 220b and output wires 230, the latter by turn being connected to sample-and-hold amplifiers (read circuits) 235 and reset circuits 237. The scan switches are also connected to sensors 210, high voltage sources 212, storage capacitors 214 and overvoltage protection elements (protection diodes) 240.
With an electromagnetic wave detector of the above described type having a circuit configuration that comprises storage capacitors for storing the generated electric charge, from which the stored electric charge is read out, a residual electric charge can be left in the detector after reading the electric charge from the storage capacitors. Then, the residual electric charge is added to the electric charge stored in the next cycle to give rise to a problem of after image when moving images are involved. Additionally, if the storage capacitors are loaded excessively with electric charge, the excessive charge can leak out to the read circuit to give rise to a phenomenon like that of blooming in a CCD image sensor. This phenomenon is particularly remarkable when the detector detects electromagnetic waves such as X rays whose energy level is higher than visible light.
Additionally, when transistors for reading the stored electric charge are formed in a bulk by using a monocrystalline wafer, electric charges unintentionally generated by high energy electromagnetic waves in the bulk can adversely affect the transistors to make them no longer operate properly.